1. Field of the Invention
This invention relates to a photoelectric current log-compression circuit, and more particularly to an improvement in a circuit for log-compressing a photoelectric current. The present invention is particularly concerned with a temperature compensating means in a photoelectric current log-compression circuit.
2. Description of the Prior Art
It has been known in the art to use a diode for log-compressing a photoelectric current utilizing the logarithmic relationship between the forward current and the forward voltage of the diode. The current-voltage relationship of the diode is changed as the temperature changes. The rate of change of the current-voltage relation accompanying the change in temperature, however, changes as the forward current flowing through the diode changes. Therefore, in the log-compression circuit using a diode the degree of the temperature compensation should be changed as the forward current flowing through the diode changes.
In order to effect the above result, it has been known in the prior art to compensate the log-compressed output for the temperature influence on the log-conversion diode by means of the forward voltage of the diode and compensate the same for the variation in the forward current flowing through the diode by means of a thermistor or the like.
The above described conventional circuit is disadvantageous in that at least two operational amplifiers are necessitated and accordingly the structure thereof becomes complicated.